In any type of home target system one of the most important elements is the means whereby the projectile is trapped. This means must be capable of absorbing sufficient of the projectiles' kinetic energy such that rebound and/or ricocheting does not occur. This is most important when projectiles such as steel BB's are used, since they do not lose kinetic energy through distortion upon impact.
An additional matter which increases the complexity of the energy absorption involves the angle at which the projectile strikes the kinetic energy absorption means in the target system. As is apparent, the height and position of the shooter with respect to the target system allows for a multiplicity of different possible paths which the projectile may take on its way to contact with the kinetic energy absorption means.
In short, once a projectile has entered the trap system regardless of the angle, means must be provided to absorb its kinetic energy whereby entrapment is insured.
However, factors which must be considered with entrapment are: weight; mobility; cost; replacement of parts; prolonged life; ease of detecting hits; reuse of the projectiles; and noise.